Surface hardening for hammermill hammers



July 24, 1962 H. F. EILERS 3,045,934

SURFACE HARDENING FOR HAMMERMILL HAMMERS Filed Aug. 18, 1961 United States Patent l 3,045,934 SURFACE HARDENING FR HAMMERMILL HAMMERS Howard F. Eilers, St. Paul, Minn., assigner to Paper Cahnenson & Co., a corporation of Minnesota Filed Aug. 18, 1961, Ser. No. 132,467 7 Claims. (Cl. 241-197) This invention relates to hammermill hammers of the type having one or more face portions which, when in use, are subjected to abrasive and impact forces directed longitudinally of the working face or faces. The invention also includes an improved method of forming or building up hard faces on such hammers.

`In the manufacture of hammermill hammers considerations of cost are of paramount importance. The hammers must be of low cost and suitable for mass production because large numbers of them are used in clusters in each hammermill and the life of the individual hammers is such that periodic replacement is necessary. To make it feasible to shape the individual hammers by inexpensive shearing and punching operations, steel stock not exceeding @ne inch thick is used and the hammers are commonly provided in thickness ranging from 1/8 inch to inch and widths not exceeding 3 inches. To provide commercially acceptable durability they must be made of shock resistant steel and should be provided with surface hardening to increase their resistance to abrasion. In hammermills, clusters of such hammers are pivotally suspended from a suitable support fitting in an opening in each hammer near one end so that the other end portion of the hammer is subject, when in use, to severe abrasive and shock forces directed longitudinally of the working end portion of the hammer. The positions of the hammers in the mill are changed from time to time when the wear at any corner or end portion has progressed to a degree where the hammer becomes inefcient or ineffective to perform its normal function.

Heretofore the effectiveness of such hard facing material has been seriously limited due to the ditiiculties attendant upon applying such material in suiiicient quantity and in fusing it to the steel hammer body with suflicient strength to prevent the spalling or breaking away of the hardening material under the forces tending to dislodge it even before the face hardening has been undercut in normal use.

It is, therefore, an object of my invention to provide a hammer of the class described of thickness in the range one-eighth inch to three-eighths inch, having a hard face of thickness Within a critical range `and greatly improved durability and resistance to shock, adapted to be applied in molten condition to the body of the hammer.

A particular object is to provide a working face portion of such a hammer comprising a layer of extremely hard, abrasion resistant material having a thermal bond with a steel body and extending in interlocking relation to a row of teeth projecting from the steel body of the hammer whereby the area of fusion between the face hardening material and the steel body is greatly extended, the useful life of the hammer is greatly increased and greatly increased resistance to impact forces directed longitudinally of the working face and acrossways of the teeth is obtained,

A further object is to provide a novel low cost method of building up hard faces of the character described on steel hammermill hammers of flat, generally rectangular shape and thickness suitable for formation by punching or shearing operations.

The invention also includes other novel features of construction which will be more fully pointed out in the following specication and claims.

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Referring to the accompanying drawings:

FIGURE l is a perspective View showing a hammermill hammer embodying my invention, one corner portion of the hammer being shown worn away as after a period of use;

FIGURES 2 and 3 are schematic, perspective views illustrating the approximate upper and lower practical limits of the proportions and dimensions of the face hardening material and steel teeth of hammers embodying my inventions;

FIGURE 4 is a plan view showing fragmentary end portions of adjoining hammers after a length of steel bar stock has been severed by a typical punching operation to form teeth on the ends of the hammer bodies, and

FIGURE 5 illustrates, diagrammatically, my preferred method for applying and building up molten hardening material on a multiplicity of hammer bodies held in a suitable fixture.

Referring to FIGURE l, my improved hammer has a steel body 6 of suitable thickness and generally rectangular form. Extending through this body at suitable spaced intervals along its longitudinal median line are openings 7 adapted to receive members for pivotally supporting the hammer in the mill in accordance with conventional practice. The body 6 is a short section of steel bar stock which has been cut to suitable length by a punching operation or shearing operation, using a parting die.

As further shown in FIGURE l, my hammer has at each end a row of teeth S of depth and pitch as hereinafter described. Hard face material 9 fills the spaces between the teeth 8 and extends to a level substantially above these teeth. The material 9 may be of any of the types hereinafter described adapted to be applied to the working face of the hammer in molten state and to be secured by a thermal bond to the entire elongated area defined by the teeth 8 and surfaces between them.

It will be evident that the teeth 8 interlock with the material 9 and greatly increase the area of thermal bond with the steel body 6. By this construction I greatly increase the resistance to spalling or breaking away of the relatively hard brittle material 9 when subjected to the shock and abrasive forces which are directed longitudinally of the end surfaces of the hammer when in use. A number of hard face materials suitable for my use are known to the Iart. The tungsten carbide type is preferred, and as commercially available, comprises ya hollow steel tube containing crushed particles of tungsten carbide of suitable screen sizes. The resultant deposit consists of granules of almost diamondahard tungsten carbide distributed in a matrix of tough steel. These deposits are both abrasion and shock resistant. A preferred grade of rods contain 60% tungsten carbide and 40% steel (by weight). The resulting hardness obtained from this composite facing is Rockell A-9l. The trade names of such material are Haynes Haystellite No. 60, Amsco Tube Tungsite, Sttoody Tube Borium, and Victor Victortube Another suitable type of hardfacing material comprises certain of the iron alloys of chromium, molybdenum, cobalt and carbon. One such alloy contains 28% chromium, 3.00% carbon, 16.0% molybdenum, 6.25% cobalt, 1.90% vanadium and the balance iron, The resulting hardness of the deposit is Rockwell C-62. This alloy is available under the trade names Haynes No. 93 Alloys, Lincolns Paceweld No. 1, Sight Feed Generator Co.s Rexarc CB, and Alloy Rods Co.s Wear-Flame No. 40.

The form of the teeth 8 may be varied, butin order to secure the advantages of the present invention the depth and pitch of these teeth in relation to the thickness of the hammer is critical within certain limi-ts if the hammers are to be formed by economical punching or shearing 3 operations. Thus from a practical viewpoint, the pitch P, viz., the center `to center spacing of the teeth along the ends of the hammer, may not be less than the thickness T of the steel hammer body (FIGS. 2 and 3 Preferably the pitch is somewhat greater than the thickness of the steel body and may, without losing the entire benefits of the invention, be made as great as twice the thickness T of the hammer. The depth of the teeth is also related to the pitch and thickness of the hammer. The depth D must not exceed the pitch `and is preferably approximately onehalf the pitch for hammers of one-quarter inch thickness as illustrated in FIG. 3. These lower limits for the pitch and upper limits of depth of teeth are imposed by the necessity for making the hammers of fairly hard shockresistant steel and the difficulties attendant upon punching or shearing such steel using parting dies of thickness or diameter less than the thickness of the steel bar stock.

The width of the elongated bar stock corresponding to the length of the working face of the hammer, indicated by the dimension L, FIG. l, may vary from two 'to three inches but for most hammermills the preferred hammer width is two inches. A half tooth 8a is provided at each corner of the steel body 6, and a practical range of the pitch P is from one-half inch to one-quarter inch for hammers of a quarter inch thickness. Thus hammers of a two inch width have from four to eight teeth and the depth D of the teeth is from one-quarter inch to oneeighth inch, approximately.

As further shown in FIGS. 2 and 3, the hard face material 9 covers the teeth 8 to a depth indicated by the dimension C which may range from one-quarter inch to oneeighth inch, ldepending on the surface tension of the face material when it is applied to the teeth in a molten state, as hereinafter described with reference to FIG. 5. The total depth of the hard face material, indicated by Athe dimension F, FIGS. 2 `and 3, is equal to the sum of the dimensions C Iand D. It has been found that any increase in the depth of this hard face, that might be provided by increasing the dimension C to a depth greater than the depth D of the teeth, results in a waste of hard face material without materially increasing the life of the hammers.

FIG. 4 illus-trates the punching operation whereby teeth are formed on the adjoining ends of each of a series of hammer bodies y6 formed from bar stock of suitable thickness. The bar stock is severed transversely by a parting die of the shape indicated at 10 for the form of the invention shown in FIG. l, thus forming teeth 8 of the required pitch and depth. This method of forming the individual hammer bodies is extremely economical in that it does not substantially increase the cost of the hammers as compared with the shearing operation required to form straight ends on each hammer.

According to my improved method, a multiplicity of the steel hammer bodies formed as indicated in FIG. 4 yare pressed together in a suitable fixture 11 `as indicated diagrammatically in FIG. 5. This fixture has a cavity adapted to receive andi fit a predetermined number of the hammer bodies 6 in face to face contact one with another, and also has suitable clamping means 12 for securing a multiplicity of hammers in such position that the teeth 8 on an end of each project upwardly substantially to a common horizontal plane. The hard face material 9 is then zapplied in molten state quickly and easily to the entire group of hammer bodies. An oxygenacetylene flame may be used to we the end surfaces of the hammer bodies by heating the steel to a critical temperature and, then, at that instant, a suitable molten face material or steel tube containing it may be melted hard surfacing compound or alloy is applied. The hard by the use of an oxygen-acetylene flame.

An example of suitable procedure is indicated diagrammatically in FIG. 5 wherein it is assumed that ame heads 1-3 and 14 are movable horizontally across and above the upper ends of the hammer bodies 6 held in the fixture 11. These heads are supplied with suitable head 13. Rods 16 of such material are fed into the head 13, as required, so that proper distribution of the molten material 9 proceeds rapidly and continuously until the desired thickness of such material has been built-up. In this manner the level of the hard face material is built up to a depth above the teeth not substantially greater than the depth of the teeth 8, as indicated at C in FIGS. 2 and 3. The surface tension of the molten material makes this feasible. `In practice, the depth of the layer C overlying the tops of the teeth 8 is limited by the surface tension of the particular molten hardening material which is built up on the toothed face of the hammers. The excess molten material ilows over the ends of the rows of teeth when the depth C equals about one-eighth -inch to about one-quarter inch. After the hard face material has solidified, the several hammer bodies of the group are separated by suitable means. This may require the application of force as by the use of a chisel to break them apart in planes such as those indicated by broken lines 9a in FIG. 5. The greatly increased thickness of the hardening material thus obtainable is in part the result of the resistance offered by the teeth on the hammer bodies to lateral flow of the molten material.

The effect of a period of use of my improved hammer is illustrated in FIG. l ywherein one corner portion of the hammer is shown worn away at 17 so that there is a sharp cutting edge 18 presented for impact with the material in the mill. Thorough tests and extensive commercial operations have demonstrated that, as compared with conventional hammers, the life of my improved hammers is greatly increased, their efficiency in operation is greatly improved and they have much improved resistance to the breaking away of the hard face material from the shock-resistant steel bodies of the hammers.

The average life of my improved hammers is approximately 2.3 times longer than the life of ordinary harnmers having face hardening approximately 1/16 inch thick along their working faces. These advantageous features of my invention are obtained at an increase in the cost for the hard :face material equal to approximately 50% over the cost of the lesser amount of the same hard facing fused to the faces of the ordinary hammers having straight end surfaces.

I claim:

1. A hammermill hammer comprising, a shock resistant steel body having an elongated working end portion of thickness in the range 1/8 inch to 3A inch subject to impact forces directed longitudinally of said working end portion and formed with a row of teeth having a pitch not substantially greater than one-half inch and not substantially less than one-quarter inch, the depth of said teeth being not substantially greater than one-quarter inch and not substantially less than one-eighth inch; and a relatively hard face material filling the spaces 'between the teeth and forming a hard working face extending to a thickness above the teeth not substantially greater than the depth of the teeth and not substantially less than one-half the depth of the teeth, said face material being joined by a thermal bond directly to said body over the entire elongated surface defined by said teeth and the surface areas between them.

2. A hammermill hammer in accordance with claim l in which said steel body is of flat generally rectangular shape and substantially uniform thickness. i

3. A hammermill hammer in accordance with claim l having a half tooth at each corner of said body and a plurality of whole teeth -between the corner teeth along each of the working end portions of said body.

4. A hammermill hammer in accordance with claim 1 in which said hard durable face material comprises an iron base alloy of approximately Rockwell C-62 hardness and having a melting point below the temperature of an Oxy-acetylene flame.

5. A hammermill hammer in accordance with claim 1 in which said relatively hard durable lface material comprises tungsten carbide particles in a shock resistant steel matrix.

6. A hammermill hammer in accordance with claim 5 in which said tungsten carbide particles comprise a major fraction, by weight, of the hard face material.

7. A hammermill hammer comprising, a shock resistant steel body having an elongated working end portion of substantially uniform thickness within the range s inch to 1%.; inch subject to impact #forces directed longitudinally of said Working end portion and formed with `a row of teeth having a pitch not less than the thickness of said end portion of said lbody and not greater than twice the thickness of said end portion, the depth of said teeth lbeing approximately one-half the pitch, and a relatively hard durable facing material filling the spaces between said teeth and forming a hard working =face portion of the hammer extending above said teeth to 4provide a surface layer of facing material of thickness not substantially greater than the depth of said teeth, said face material being joined by a thermal bond directly to said body over the entire elongated surface deined by said teeth and the surface areas between them.

References Cited in the file of this patent UNITED STATES PATENTS 1,974,215 Kilmer Sept. 18, 1934 2,607,538 Larson Aug. 19, 1952 2,763,439 =Mask0ff Sept. 18, 1956 FOREIGN PATENTS 686,499 Germany Ian. 11, v1940 

